Don't truncate and replace with 'a', update docs

builder/googlecompute/template_funcs.go

@@ -16,17 +16,13 @@ func isalphanumeric(b byte) bool {
 }
 
 // Clean up image name by replacing invalid characters with "-"
-// truncate up to 63 length, convert to a lower case
+// and converting upper cases to lower cases
 func templateCleanImageName(s string) string {
 	if reImageFamily.MatchString(s) {
 		return s
 	}
 	b := []byte(strings.ToLower(s))
-	l := 63
-	if len(b) < 63 {
-		l = len(b)
-	}
-	newb := make([]byte, l)
+	newb := make([]byte, len(b))
 	for i := range newb {
 		if isalphanumeric(b[i]) {
 			newb[i] = b[i]
@@ -34,12 +30,6 @@ func templateCleanImageName(s string) string {
 			newb[i] = '-'
 		}
 	}
-	if !('a' <= newb[0] && newb[0] <= 'z') {
-		newb[0] = 'a'
-	}
-	if newb[l-1] == '-' {
-		newb[l-1] = 'a'
-	}
 	return string(newb)
 }
 

builder/googlecompute/template_funcs_test.go

@@ -19,18 +19,6 @@ func Test_templateCleanImageName(t *testing.T) {
 			origName: "abcde-012345v1.0.0",
 			expected: "abcde-012345v1-0-0",
 		},
-		{
-			origName: "a123456789012345678901234567890123456789012345678901234567890123456789",
-			expected: "a12345678901234567890123456789012345678901234567890123456789012",
-		},
-		{
-			origName: "01234567890123456789012345678901234567890123456789012345678901.",
-			expected: "a1234567890123456789012345678901234567890123456789012345678901a",
-		},
-		{
-			origName: "01234567890123456789012345678901234567890123456789012345678901-",
-			expected: "a1234567890123456789012345678901234567890123456789012345678901a",
-		},
 	}
 
 	for _, v := range vals {

website/source/docs/templates/engine.html.md

@@ -53,9 +53,12 @@ Here is a full list of the available functions for reference.
 #### Specific to Google Compute builders:
 
 -   `clean_image_name` - GCE image names can only contain certain characters and
-    the maximum length is 63. This function will replace illegal characters with a "-" character
-    and truncate a name which exceeds maximum length.
-    Example usage since ":" is not a legal image name is: `{{isotime | clean_image_name}}`.
+    the maximum length is 63. This function will convert upper cases to lower cases
+    and replace illegal characters with a "-" character.
+    Example usage since ":" is not a legal image name is: `"a-{{isotime | clean_image_name}}"` -> `a-2017-10-18t02-06-30z`.
+
+    Note that image name must be a match of regex `(?:[a-z](?:[-a-z0-9]{0,61}[a-z0-9])?)`
+    but this function won't truncate and replace with valid character such as 'a' except '-'.
 
 ## Template variables